The present invention relates to a drive apparatus such as a magneto-optical disk or an over-writable optical disk, and more particularly to generation of data write/read clocks.
Synchronization signals and sector addresses are recorded as prepit trains in the magneto-optical disk or the over-writable optical disk (hereinafter simply referred to as a disk). When data is to be written into such a disk, the prepit trains are read to generate the synchronization signals, a write clock is generated based on the synchronization signals, and the data write timing is attained by the clock. As a result, the data is written into the disk in synchronism with the synchronization signal. When the data is to be read from the disk, the prepit trains are read to reproduce the synchronization signals, and the read clock for reproducing the data is generated based on the synchronization signal.
When the data is written into the disk, it is necessary to check whether the data has been written correctly. To this end, the drive apparatus which permits writing and reading of data on a writable disk is provided with a direct read-after-write (DRAW) function to read the data simultaneously with the writing of the data in order to check the correctness of the data writing.
In order to effect the DRAW, a write laser beam, having sufficient power and a read laser beam which has sufficient power to read the data but does not destroy the data on the disk, are required. In a write mode in which the data is written into the disk, the data is written by the write laser beam and the written data is read by the read laser beam. The prepit trains on the disk are also read by the write laser beam, and the write clock is generated based on the reproduced synchronization signals. In a read mode in which the data written on the disk is read, the write laser beam is turned off and the data is read by the read data beam.
In this manner, the DRAW is attained. In the prior art, it is common to use separate light sources for the write laser beam and the read laser beam. Thus, two laser sources are used to write and read the data.
On the other hand, a technique to generate 0-order light, i.e. the strongest light beam, and 1-order light, i.e. the second strongest light beam, from an output light of a single laser source by a diffraction grating in order to attain the DRAW is known by, for example, JP-A-62-252552. In the prior art, data is written and read into and from a magneto-optical recording medium. A single semiconductor laser, 0-order light (or main beam) and two 1-order lights (or sub beams) are generated from the single laser beam emitted from the semiconductor laser by a diffraction grating. The laser beams are directed to the magneto-optical recording medium. Radiation positions of the laser beams are set such that a spot of one of the 1-order lights is ahead of a spot of the 0-order light while a spot of the other 1-order light is behind the spot of the 0-order light. In the write mode, the 0-order light is used with a magnetic field from a magnetic field generation device to write data into the magneto-optical recording medium, the 1-order light whose spot is ahead of the spot of the 0-order light is used to read an address previously written in the magneto-optical recording medium, and the 1-order light whose spot is behind the spot of the 0-order light is used to read the data written by the 0-order light. In this manner, the DRAW is attained. In the data read mode, the 0-order light is used.
An example of generation of a write clock and a read clock in a disk drive apparatus is explained with reference to FIG. 2. Numeral 1 denotes a disk, numeral 2 denotes a 0-order light optical pickup, numeral 3 denotes a 1-order light optical pickup, numerals 4 and 5 denote preamplifiers, numerals 6 and 7 denote binarization circuits, and numerals 8 and 9 denote synchronization circuits.
In a write mode, an output power of a laser source (not shown) is increased. 0-order light is used for writing and 1-order light is used for reading. A reflected light of the 0-order light from the disk 1 is sensed by the optical pickup 2 and an output signal thereof produced by a prepit train on the disk 1 is amplified by the preamplifier 4 and reshaped by the binarization circuit 6 for each prepit on the disk 1. The synchronization signal thus produced is supplied to the synchronization circuit 8 which includes a PLL circuit and a write clock is generated in synchronism with the synchronization signal. Similarly, a reflected light of the 1-order light from the disk 1 is sensed by the optical pick-up 3, and an output signal thereof produced by the prepit train is amplified by the preamplifier 5, and the amplified signal is reshaped by the binarization circuit 7 so that a synchronization signal is produced. The synchronization signal is supplied to the synchronization circuit 9 which includes a PLL circuit, which generates a read clock in synchronism with the synchronization signal.
In this manner, the data writing by the 0-order light and the data reading by the 1-order light are attained.
In the disk drive apparatus shown in FIG. 2, however, it is necessary to prevent the data on the disk from being destroyed by the 0-order light in the read mode. To this end, the 0-order light may be blocked, but it is very difficult to block only the 0-order light because the 0-order light and the 1-order light are very closely located to each other. Accordingly, it is necessary to reduce the output power of the laser source to reduce the power of the 0-order light in the read mode. However, the power of the 1-order light is also reduced by decreasing the output of the laser source. The binarization circuit 7 may not correctly reproduce the synchronization signal because the output level of the optical pickup 3 produced by reading the prepit train is too low.
Because the 0-order light has a sufficient power to read the data, the 0-order light may be used to read the data in the read mode, the prepit train may be read by the 0-order light to reproduce the synchronization signal by the binarization circuit 6, and the clock produced by the synchronization circuit 8 based on the synchronization signal may be used as the read clock.
However, when the mode is switched from the read mode to the write mode, the 0-order light used to read the data in the read mode is used to write the data in the write mode, and the 1-order light is used to read the data, instead. Thus, when the mode is switched from the read mode to the write mode, the data read laser beam is switched from the 0-order light to the 1-order light. Accordingly, when the mode is switched, the read clock is switched from the output of the synchronization circuit 8 to the output of the synchronization circuit 9. Until immediately before the mode switching, the synchronization circuit 9 does not receive the correct synchronization signal because the output level of the optical pickup 3 is insufficient and the synchronization circuit 9 cannot immediately respond to a correct synchronization signal supplied from the binarization circuit 7 after the mode switching. Thus, a long pull-in time to the synchronization signal is required, and recording cannot be initiated until the pull-in is completed and a corresponding recording area is wasted. This prevents high density recording of the data.
Where two light sources are used, there are economical and practical problems such as high manufacturing cost and large size of the apparatus because each of the optical pickups is provided with the synchronization circuit.